Quantitative fluorescent speckle microscopy: where it came from and where it is going

Fluorescent speckle microscopy (FSM) is a technology for analysing the dynamics of macromolecular assemblies. Originally, the effect of random speckle formation was discovered with microtubules. Since then, the method has been expanded to other proteins of the cytoskeleton such as f-actin and microtubule binding proteins. Newly developed, specialized software for analysing speckle movement and photometric fluctuation in the context of polymer transport and turnover has turned FSM into a powerful method for the study of cytoskeletal dynamics in cell migration, division, morphogenesis and neuronal path finding. In all these settings, FSM serves as the quantitative readout to link molecular and genetic interventions to complete maps of the cytoskeleton dynamics and thus can be used for the systematic deciphering of molecular regulation of the cytoskeleton. Fully automated FSM assays can also be applied to live-cell screens for toxins, chemicals, drugs and genes that affect cytoskeletal dynamics. We envision that FSM has the potential to become a core tool in automated, cell-based molecular diagnostics in cases where variations in cytoskeletal dynamics are a sensitive signal for the state of a disease, or the activity of a molecular perturbant. In this paper, we review the origins of FSM, discuss these most recent technical developments and give a glimpse to future directions and potentials of FSM. It is written as a complement to the recent review (Waterman-Storer & Danuser, 2002, Curr. Biol., 12, R633-R640), in which we emphasized the use of FSM in cell biological applications. Here, we focus on the technical aspects of making FSM a quantitative method.